1. Field of the Invention
The present invention relates to a method of forming a tentative surface protective coating cured by irradiation with an ultraviolet ray, an ultraviolet ray-curable rubbery elastomer, and a screen ink using the elastomer. More particularly, the present invention relates to a method of forming a tentative surface protective coating which is used for selectively surface treating a surface of a substance such as, a copper coated integrated plate usable to a printed circuit substrate, a steel plate, an aluminum plate, and a copper plate, a quartz plate, a glass plate, other inorganic substance, and organic substance by means of a surface treating method such as, electrolytic plating, electroless plating, soldering and the like, a rubbery elastomer which is used in the method, and a screen ink using the elastomer.
2. Related Art Statement
Heretofore, as surface treating methods such as, electrolytic plating, electroless plating and soldering, there have been known the following methods:
1 a method wherein a surface of a desired substance to be surface treated having an inorganic surface is placarded with an adhesive tape consisting of a crape paper or a polyester film and an adhesive layer laminated thereon, immersed in a plating liquid or a soldering liquid, subjected to a desired plating or soldering treatment, taken out from the liquid, cooled to ambient temperature, removed from the adhesive tape by peeling, rinsed by a rinsing solvent such as Freon (trade name of a commercial fluorohydrocarbon made by Du Pont Co.) etc., and dried to complete the method;
2 a method wherein a surface of a desired substance to be surface treated having an inorganic surface is heated and placarded with a dry film type photoresist material which is used for plating (a commercial product sold by Asahi Chemical Industry Co., Ltd. etc.), masked intimately by a nega or posi type photomask, cured by irradiation with an ultraviolet ray, removed from the photomask, developed at the uncured portions by means of a developer such as an alkaline aqueous solution, etc., or an organic solvent, dried by heating or irradiation with an infrared ray, etc., to form a tentative surface protective coating thereon, immersed in a plating or soldering liquid, subjected to a desired plating or soldering treatment, taken out from the liquid, cooled to ambient temperature, removed from the tentative surface protective coating by means of a peeling-off solution determined exclusively for the above dry film type photoresist material, such as an organic solvent, e.g., methylene chloride, trichloroethylene, etc., or a strong alkaline aqueous solution, e.g., a sodium hydroxide aqueous solution, rinsed by water, etc., and dried to complete the method;
3 a method wherein a surface of a desired substance to be surface treated having an inorganic surface is coated with a solution of photoresist material in an organic solvent which is used for plating (a commercial product sold by Tokyo Ouka Kogyo K.K., etc.) by means of a coating machine such as spin coater, dried by a heating drying machine such as drier to remove the organic solvent, masked intimately by a nega or posi type photomask, cured by irradiation with an ultraviolet ray, removed from the photomask, developed at the uncured portions by means of a developer such as an alkaline aqueous solution, etc., or an organic solvent, dried by heating or irradiation with an infrared ray, etc. to form a tentative surface protective coating, immersed in a plating or soldering liquid, subjected to a desired plating or soldering treatment, taken out from the liquid, cooled to ambient temperature, removed from the tentative surface protective coating by means of a peeling-off solution determined exclusively for the above dry film type photoresist material, such as an organic solvent, e.g., methylene chloride, trichloroethylene, or a strong alkaline aqueous solution, e.g., a sodium hydroxide aqueous solution, rinsed with water, etc., and dried to complete the method; and
4 a method wherein a surface of a desired substance to be surface treated having an inorganic surface is printed with a thermosetting screen printing ink by screen printing, heat treated to form a tentative surface protective coating, immersed in a plating or soldering liquid, subjected to a desired plating or soldering treatment, taken out from the liquid, cooled to ambient temperature, peeled off physically from the tentative surface protective coating to complete the method.
The above described prior methods have many drawbacks as follows.
The prior method 1 of placarding the adhesive tape on the inorganic surface of the substance to be surface treated is economical in cost. However, the tape has an inferior chemical resistance to the plating liquid, so that it is frequently peeled off during the plating step, or the tape is melted on the inorganic surface due to the use of the soldering liquid at a high temperature of 250.degree.-260.degree. C., so that, when the adhesive tape is peeled from the inorganic surface, the adhesive agent of the tape is transferred to the inorganic surface to remain thereon, which adhesive agent is very difficult to remove. Moreover, if the areas of the inorganic surface of the substance to be placarded by the adhesive tape exist are scattered on the inorganic surface, the tape has to be cut to the respective size of the areas and has to be placarded on the areas one by one, so that these procedures are very cumbersome and troublesome.
The prior method 2 of heating the inorganic surface and placarding the surface with the dry film type photoresist material requires an exclusive laminating machine for the heating and placarding, and an exclusive developer machine and an exclusive draft chamber for dealing with the developer liquid containing a noxious organic solvent or alkaline aqueous solution. In addition, the developer liquid used for developing the uncured photoresist material has to be substituted after a long use period by a new developer liquid, and the old developer liquid has to be processed and discarded. Moreover, the method is laborsome in that it needs the drying treatment using the heating or infrared ray irradiation after the developing treatment. Furthermore, the method is laborsome and cumbersome in that it requires the exclusive liquid for peeling off the tentative surface protective coating from the inorganic surface after the plating or soldering treatment.
The prior method 3 of coating the inorganic surface of the substance to be surface treated with the solution of photoresist material in an organic solvent has to arrange an exclusive developer liquid and a ventilation equipment such as a draft chamber, because apparatuses for applying and drying the solution of photoresist material, ventilation equipments such as a draft chamber, and the developer liquid for the developing treatment deal with a noxious organic solvent or an alkaline aqueous solution. In addition, the developer liquid used for developing the uncured photoresist material has to be substituted after a long use period by a new developer liquid, and the old developer liquid has to be processed and discarded. Moreover, the method is laborsome in that it needs the drying treatment using the heating or infrared radiation after the developing treatment. Furthermore, the method is laborsome and cumbersome in that it requires the exclusive liquid for peeling off the tentative surface protective coating from the inorganic surface after the plating or soldering treatment.
The prior method 4 of screen printing the inorganic surface of the substance to be surface treated with the thermosetting screen printing ink can obviate the above drawbacks of prior methods 1-3, because the tentative surface protective coating is formed by screen printing and heat treatment so that both the cumbersome developing treatment and the expensive equipment necessary for the developing treatment can be dispensed with, and the tentative surface protective coating can be easily peeled off manually. However, if a substrate of a laminar structure made of a thin copper layer and a paper layer impregnated with a phenolic resin or a glass layer impregnated with an epoxy resin tightly adhered to each other by an adhesive is used as a printed circuit substrate, the substrate is deformed due to differences of thermal expansion coefficients of the layers at the time of heat curing the screen printed ink, so that the plating or soldering treatment of the screen printed substrate is adversely influenced and difficult to be achieved with good precision. Moreover, the method has a drawback of necessitating a little long curing time of at least 5-10 min. in case of heat curing.